Drip chamber with air vent

Claim 1

An intravenous set comprising a volume limiting chamber for controlling the volume of parenteral solution administered to a patient and a drip chamber positioned downstream of said volume limiting chamber for determining the parenteral solution flow rate, said drip chamber comprising a transparent, flexible chamber, inlet means associated with one end of said transparent, flexible chamber for receiving a parenteral solution from said volume limiting chamber, said inlet means defining a drop-forming orifice for forming said parenteral solution into drops of a predetermined size, and outlet means associated with the other end of said transparent, flexible chamber, said outlet means adapted to discharge said parenteral solution from said transparent chamber, said volume limiting chamber having a membrane valve positioned in said volume limiting chamber so that all parenteral solution in said volume limiting chamber flows through said membrane valve, said membrane valve comprising a material which when wet will pass parenteral solution but will not pass air at normal intravenous administration pressures, and air vent means communicating directly with the interior of said drip chamber for selectively placing said drip chamber in communication with the atmosphere when said membrane valve is wet and said drip chamber is at least partially filled with parenteral solution, said air vent means comprising an air passage communicating directly with the interior of said drip chamber, said drip chamber, said membrane valve, and said air vent means each operable in a first mode for simultaneously evacuating a first volume of air from said drip chamber directly to the atmosphere without rupturing said membrane valve, and preventing parenteral solution contained in said volume limiting chamber from entering said drip chamber, each operable in a second mode for introducing a volume of parenteral solution from said volume limiting chamber into said drip chamber to substantially replace said first volume of air evacuated from said drip chamber during said first mode, and each operable in a third mode for simultaneously admitting a second volume of air directly from the atmosphere into said drip chamber, preventing parenteral solution contained in said volume limiting chamber from entering said drip chamber, and removing a volume of liquid through said outlet means, said volume of liquid being substantially equal to said second volume of air.